UAV4GEO Thermal tool question

Hi Alessio! What sensor and SDK version are you using? I might be able to share my experience as I have been through this myself recently

EDIT: apologies I did not check the SDK version in ThermalTools. I will continue with my reply in a bit

Thanks a lot for te answer. I tried converting the thermal images we acquired with UAV4GEO setting the distance at 25 m but when i tried to open them on QGIS to visualize the result i noticed that the converted images had a wrong coordinate metadata (the images had no projection set and when i specified the reference system they were all overlapped. I tried opening the metadata of the converted images and the coordinates are correct but in QGIS they are not applied) and also the number of pixel in the converted image has been halved (the original image was 1280x1024 while the converted one was 640x512). Did you or someone else have the same problem?

I think you're expecting the tool to georeference/reproject the thermal images as GeoTIFF, but that's not what the tool does, ThermalTools extracts the celsius values (which are 640x512) to a standard 32bit TIFF and copies the EXIF meta from the original image. If you want to see the results on a map, first process the images with WebODM.

Thanks for the clarification, insetad for the cap of 25 m tò the acquisition distance Is there a way to raise the distance value? And of not how does the distance impact on the result of the conversion with a distance of acquisition that is much higher than the limit (we flew at around 200-250 metres)?

The distance 25 m is unfortunately the capped maximum. I am not familiar with the SDK binaries and maybe it would be possible to tinker with it, but I am not sure if it would be a right direction. I think all we can do with DJI thermal sensors is just to simulate what the distance parameter does to the measurements. Once upon a time I was reading through some forums to see if someone had managed to reverse-engineer the equations for H20T's radiometric calibration but I didn't find anything...

Honestly I am not sure why it is capped to 25 m. Could it be that they had some specific industrial applications in mind?

I am however going to run some experiments; I have some more datasets of the same study area taken at 50 m AGL and 100 m AGL. I will take a look at what the distance parameter does to the water patches taken from these altitudes and share it here. It should change things a bit as the reflected radiance has to travel a longer path through the atmosphere to reach the sensor

FWIW I wonder if the thermal cap of 25m is a matter of calibration and manufacturing production. These thermal sensors are affected by ambient environment and sensor sizes. Not unlike regular rgb camera sensor size dictates the megapixel value and how much light is possible to capture. Both sensors can take photos from any distance but pixel value and resolution is limited by sensor sizes.
With thermal the resolution is already much less than an rgb camera in the same machine and determining accurate radiance is impacted. Then processing the captured results to models and maps is a matter of sfm/ODM doing the best it can on lower resolution pixels.
Also I was once told for these cameras to effectively detect thermal difference the subjects need to have a certain temperature difference for the sensor to detect thermal difference. If a subject (person) is 98deg f and the ambient environment (ground) is also 98deg f then the sensor detects all of the radiance as the same value. That could also be an impacted factor with 25m cap and results.